'Ultimate' Just-in-case LiveUSB distro?

I have a LiveUSB of Xubuntu 11.04 that I used for the installation onto my HD a while back. It seems to boot and run fine in Live ('Try') mode, so I'm perfectly fine with keeping it around 'just in case,' or as a handy way to carry a personal desktop environment around and just boot off that if I'm using a different computer.

But then I wondered if there is a 'just in case' where I might want something different - ie, would I be better off with a Lubuntu LiveUSB or one from Slax, both of which would probably boot/run faster if for some reason I had to use/fix an old or broken machine? I think the most common situations would be either a "Get files from Windows, throw a small 'Buntu install on there for backup" -type thing (like when I'm helping fix someone's computer), or a "Crap, I just broke my computer and I really need to keep doing x."

Other considerations:
1) I probably want to use FAT, so that I can keep using the USB for it's usual purpose - moving files between Windows/Mac computers.
2) I will be using a 2GB flashdrive unless I pick up an 8GB in the near future.
3) I also have a 500GB external drive for backup and extra ISOs, and will probably put an install of Xubuntu on a 20GB partition (which means I should probably go with something superlightweight on the flash drive, if I can just use the 'big guy' for serious installs.

Re: 'Ultimate' Just-in-case LiveUSB distro?

I've always liked Parted Magic. There is documentation links on the left. Follow the one for "Live USB". Unetbootin is used now to make the USB version, which is simple stupid to use. http://partedmagic.com/doku.php

Re: 'Ultimate' Just-in-case LiveUSB distro?

I like Live USBs for that, but the downside I see from your use is that some older machines may not boot from usb, so keep a cd/dvd of it handy as well so that way if it won't light up from usb you canuse that to make it run from the optical drive since that will usually-to-always work on machines roughly 10 years old and newer.